The present invention relates to a roll changing device of a rolling mill of the type having an intermediate roll disposed between a work roll and a back up roll.
Such a type of rolling mill has been known as having an axially displaceable intermediate roll between a work roll and a back up roll. In this type of rolling mill, the intermediate roll is axially shifted in accordance with the width of the material to be rolled to precisely control the deflection of the work roll over the entire length regardless of the change in the factors of rolling condition such as rolling load, rolling width and so forth. In consequence, the deflection of the work roll is diminished to achieve a high shape controlling performance.
The change of rolls in this type of rolling mill has been hitherto achieved by means of a complicated roll changing device having roll changing rails for respective rolls and mounted in a housing, and delivery rails disposed at the front side of the mill at the same level as respective roll changing rails and in alignment with the latter. The rolls are exchanged between the rails inside and outside the mill housing. The frequency or demand of the change of rolls is highest with the work rolls, while the back up rolls have lowest demand or frequency of changing. From this point of view, Japanese Patent Publication No. 7615/1979 discloses a roll changing device in which the delivery rails for at least the work rolls and the intermediate rolls are mounted on a roll changing truck adapted to run on stationary rails to permit change of two work rolls or four rolls including two intermediate rolls at a time.
The scale of the rolling mill of the type described is becoming huge year by year particularly in, for example, hot strip mills. In the large-size rolling mill of the kind described, the rolls and the roll changing rails are placed at a large depth from the floor level. In the conventional roll changing device of the kind disclosed in the above-mentioned Japanese Patent Publication, therefore, it is necessary to place the roll changing truck at a large constant depth within a pit in front of the mill. In consequence, the transfer of the new and old rolls to and from the roll changing truck becomes troublesome and difficult due to a restriction in the space. This in turn impractically prolongs the time required for the change of the work roll and the intermediate rolls which have to be changed at high frequency, resulting in a reduced yield of the rolled product.